The relationships between LV force and size (i.e., pressure and volume, stress and volume, or stress and diameter) at end-systole provide a useful means of characterizing LV performance in the isolated canine heart. The purpose of the proposed research is to extend these observations to conscious animals with intact circulations, both under normal and pathophysiologic conditions. For these studies, dogs will per preinstrumented with an LV micromanometer, an inferior vena caval (IVC) cuff occluder and ultrasonic crystals for the measurement of LV major and minor axes and wall thickness; end-systolic force-size relationships will be constructed in the awake state using LVC cuff inflation, assuming a general ellipsoid for LV volume calculation. Experiments will be performed to determine the effects of acute alterations in arterial impedance, reflex control, and contractility on these relations, as well as the effects of chronic interventions which alter LV shape, mass, contractile state, and interdependence with the right ventricle, including: 1) chronic volume overloading by an arteriovenous fistula; 2) chronic pressure overloading by renovascular hypertension; 3) myocardial failure by cobalt surface administration; and 4) chronic RV pressure overloading by pulmonary artery banding. It is hoped that these studies will better define the relationship between force and size at end-systole in the intact circulation and clarify the alterations which occur with hypertrophy and failure, thereby providing a stronger basis for the clinical application of these concepts.